Lactose Intolerance, or otherwise referred to as lactose maldigestion, is the inability to digest a significant amount of lactose, derived from a deficiency of the lactase enzyme in the small intestines. Lactose is the natural sugar in milk and milk products of all mammals. Lactase is the enzyme which splits the milk sugar lactose into its components (i.e., glucose and galactose), and also breaks down the milk sugar into smaller forms that can be processed into the bloodstream. The lactase enzyme is necessary for mammals to digest lactose.
There is an important distinction between lactose intolerance and milk allergies. Lactose intolerance is the inability of the body to digest lactose containing products due to a deficiency in the lactase enzyme. A milk allergy, however, is a sensitivity to the protein in milk, which involves the immune system and does not relate to a deficiency of the lactase enzyme. In humans, a milk allergy is usually experienced only by infants.
Generally, humans develop lactose intolerance from a primary or secondary cause. The primary cause is an onset loss of lactase that is a permanent condition. This occurs at a variable period after the weaning period. The primary cause is also genetically determined. The secondary cause is generally a temporary condition that occurs as a result of another disease or event that damages the lining of the small intestine where lactase is active. This is usually caused by an acute diarrheal disease, parasitic infection, Crohn's disease, celiac disease, gastrointestinal surgery, or the intake of certain medications.
In addition to the primary and secondary causes, certain human ethnic and racial populations have more of a predisposition for lactose intolerance. In these populations, social and cultural habits and attitudes influence lactose intolerance. Lactose activity can also decrease with age in certain ethnic and racial populations, including those populations which have origins in Europe, the African plains, and the Siberian Steppes. Humans who are most likely to have or develop lactose intolerance include those of Asian, Middle Eastern, North American, African, and Latin American descent.
According to several sources, there are 30 to 50 million people in the world who are lactose intolerant. In the 1960's and 1970's, it was reported that 70% of the adults in the world had lactose intolerance. In 1995, is was reported that 75% of the adults in the world and 25% of the adults in the U.S. were categorized as being lactose intolerant. In 1994, it was reported that 75% of African Americans and Native Americans and 90% of Asian Americans had lactose intolerance. It has also been reported that 30% of adults who are mostly North Western and North American descendants of the Europeans, have adapted to high lactase activity into adulthood. Research concludes that this adaptation is genetically controlled, permanent and related to a long tradition of milk and milk products consumption in these regions of the world.
Lactose intolerance can be tested either indirectly or directly. There are three main ways to test by the indirect method: a hydrogen breath test, a stool acidity test, or a blood glucose test. In the hydrogen breath test, the breath is measured to determine the amount of hydrogen produced after consuming a measured amount of lactose, typically 15 g. The lactose is consumed by drinking a lactose mixture, and the subject exhales into a vacuum-sealed collection tube at three one hour time intervals. A high level of hydrogen in the breath indicates an improper digestion of lactose. In a stool test, the stool is tested to determine the amount of acid. In a blood glucose test, the blood is tested to determine the amount of glucose (sugar) content after administering a predetermined amount of lactose-containing product to the subject. The direct method measures lactose activity in a mucosal biopsy specimen.
If an individual suspects that he has lactose intolerance, it is potentially harmful for him to restrict his diet since it may result in a nutrition shortage or a failure to detect a more serious disease. Milk and other dairy products are major sources for nutrition in the basic American diet. The primary nutrients in milk are protein, calcium, riboflavin, vitamin A, and vitamin D. Calcium is an important part of the recommended daily allowances of vitamins and minerals and any deficiency therein can lead to osteoporosis.
When an individual has an allergic reaction to milk, there are several different resulting symptoms depending on the age of the individual. For young adults and adults, symptoms include bloating, nausea, cramps, and diarrhea, while the symptoms in infants are diarrhea, dehydration, malnutrition, and potentially death. Some of the symptoms vary based on the level of tolerance the person has, the amount and type of lactose consumed, or the remainder of the person's diet.
Lactose is not digested when the amount of lactose consumed exceeds the lactase enzyme capacity of the small intestine. Instead, excess undigested lactose passes through the small intestines into the large intestine where it is fermented by a bacteria called colinic flora. The fermentation of the lactose in the large intestine produces hydrogen and methane which can lead to bloating, gas, and diarrhea. These symptoms are caused by a very low activity of lactase in the intestines.
The use of lactase tablets which are generally available, help lactose intolerant people digest milk and milk products. Each lactase tablet typically hydrolyzes up to 99% of the ingested lactose within 24 hours, and is designed to be ingested with the lactose containing food.
Young children who have lactose intolerance are very rare. The amount of lactase enzyme a body produces generally reaches a maximum immediately after birth and then decreases in the majority of people after their body adjusts during the ages of 3–15. A stool test is used to test lactose intolerance in young children. For young children, the breath test is not as accurate because they usually have a tendency to get dehydrated which can cause diarrhea.
The reasons for an onset of lactose intolerance are generally unknown. However, there is a general belief that by consuming small amounts of lactose frequently over a period of time, lactose intolerance can be improved. Whole milk and chocolate milk appear to be tolerated better than low fat milk because the fat content of whole milk and chocolate milk slows the rate of gastric emptying. Many lactose intolerant people can have at least 8 oz of milk. Also, many lactose intolerant people can have hard cheeses because during manufacturing most of the lactose is removed with the whey. During the aging of the cheeses, the remaining lactose is converted to lactic acid and other products. As a result, most aged cheeses have little to no lactose. Some of such firm cheeses include cheddar, Swiss and mozzarella. Another product that lactose intolerant people can tolerate is yogurt, with live culture bacteria in it. Having yogurt with a non-fermented dairy product can improve lactose digestion.
People typically have different symptoms of lactose intolerance. Lactose intolerance may also be psychologically induced. There are also many different variations of lactose intolerance depending on the individual. For example, some individuals cannot have cheese, melted cheese, plain milk, or warm dairy containing products like milk in coffee, while others cannot have any dairy products at all. Also, most lactose intolerant people are limited as to the amount of special “lactose free” foods they can eat that have been manufactured by specific companies. Some examples of these “lactose free” foods are: Mocha Mix ice cream, Tofutti ice cream and ice cream sandwiches, LACTAID® brand milk, Formagg cheese, Tofutti “Better than Cream Cheese”, margarine, and live cultured yogurt. The only problem with all these products is that they are not readily available everywhere.